Signaling scaling matrices in video coding

ABSTRACT

A video decoder can be configured to receive a syntax element indicating whether chroma scaling matrices are signaled for the video data; in response to determining that chroma scaling matrices are signaled for the video data, determine a chroma scaling matrix for a block of video data; determine a block of chroma transform coefficients for the block of video data; dequantize a first chroma transform coefficient of the block of chroma transform coefficients using a first scaling value from the chroma scaling matrix; dequantize a second chroma transform coefficient of the block of chroma transform coefficients using a second scaling value from the chroma quantization matrix; and determine a chroma residual block for the block of video data based on the first dequantized chroma transform coefficients and the second dequantized chroma transform coefficient.

This application claims the benefit of U.S. Provisional PatentApplication 62/960,616, filed 13 Jan. 2020, the entire content of eachbeing incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

As will be explained in more detail below, video data can include a lumacomponent and two chroma components. In some video bitstreams, thechroma components may be sub-sampled relative to the luma component, butin other instances, the chroma components may not be sub-sampled.Additionally, in some video bitstreams the decoding of chroma componentsmay be dependent on the luma components. That is, information associatedwith the luma component may be needed to decode the chroma components.Some video bitstreams may be coded using what is referred to as separatecolor plane coding, in which these dependencies are removed, making eachcomponent independently decodable. Separate color plane coding mayreduce compression, but may also reduce encoding and decoding latencydue to the fact that the different components may be decoded inparallel, which can be desirable for real-time applications such as livestreaming, video conferencing, and the like.

This disclosure describes techniques that may improve the signalingoverhead associated with encoding and decoding chroma components ofvideo data, and more specifically, may reduce the signaling overheadassociated with signaling chroma quantization matrices. The techniquesof this disclosure may be of particular value for video bitstreams thatutilize separate color plane coding or similar coding tools. Bysignaling a syntax element indicating whether chroma quantizationmatrices are signaled for the video data a video encoding and decodingsystem may reduce signal overhead by avoiding any unnecessary signalingof chroma quantization matrices, but at the same time, maintain theflexibility of enabling and disabling the use of chroma quantizationmatrices.

According to one example of this disclosure, a method of decoding abitstream of encoded video data includes receiving, from the bitstreamof encoded video data, a syntax element indicating whether chromascaling matrices are signaled for the encoded video data; in response todetermining that chroma scaling matrices are signaled for the videodata, determining a chroma scaling matrix for a block of the encodedvideo data; determining a block of chroma transform coefficients for theblock, wherein the block of chroma transform coefficients comprises atleast a first chroma transform coefficient and a second chroma transformcoefficient; determining a quantization parameter (QP) value for theblock of chroma transform coefficients; dequantizing the first chromatransform coefficient of the block of chroma transform coefficientsusing a first scaling value from the chroma scaling matrix and based onthe QP value; dequantizing the second chroma transform coefficient ofthe block of chroma transform coefficients using a second scaling valuefrom the chroma scaling matrix and based on the QP value, wherein thesecond scaling value is different than the first scaling value;determining a chroma residual block for the block based on the firstdequantized chroma transform coefficients and the second dequantizedchroma transform coefficient; adding the chroma residual block to achroma prediction block to determine a decoded chroma block; andoutputting decoded video data that includes the decoded chroma block.

According to another example of this disclosure, a device for decodingvideo data includes a memory configured to store video data and one ormore processors implemented in circuitry and configured to: receive,from the bitstream of encoded video data, a syntax element indicatingwhether chroma scaling matrices are signaled for the encoded video data;in response to determining that chroma scaling matrices are signaled forthe video data, determine a chroma scaling matrix for a block of theencoded video data; determine a block of chroma transform coefficientsfor the block, wherein the block of chroma transform coefficientscomprises at least a first chroma transform coefficient and a secondchroma transform coefficient; determine a quantization parameter (QP)value for the block of chroma transform coefficients; dequantize thefirst chroma transform coefficient of the block of chroma transformcoefficients using a first scaling value from the chroma scaling matrixand based on the QP value; dequantize the second chroma transformcoefficient of the block of chroma transform coefficients using a secondscaling value from the chroma scaling matrix and based on the QP value,wherein the second scaling value is different than the first scalingvalue; determine a chroma residual block for the block based on thefirst dequantized chroma transform coefficients and the seconddequantized chroma transform coefficient; add the chroma residual blockto a chroma prediction block to determine a decoded chroma block; andoutput decoded video data that includes the decoded chroma block.

According to another example of this disclosure, a computer-readablestorage medium stores instructions that when executed by one or moreprocessors cause the one or more processors to: receive, from abitstream of encoded video data, a syntax element indicating whetherchroma scaling matrices are signaled for the encoded video data; inresponse to determining that chroma scaling matrices are signaled forthe video data, determine a chroma scaling matrix for a block of theencoded video data; determine a block of chroma transform coefficientsfor the block, wherein the block of chroma transform coefficientscomprises at least a first chroma transform coefficient and a secondchroma transform coefficient; determine a quantization parameter (QP)value for the block of chroma transform coefficients; dequantize thefirst chroma transform coefficient of the block of chroma transformcoefficients using a first scaling value from the chroma scaling matrixand based on the QP value; dequantize the second chroma transformcoefficient of the block of chroma transform coefficients using a secondscaling value from the chroma scaling matrix and based on the QP value,wherein the second scaling value is different than the first scalingvalue; determine a chroma residual block for the block based on thefirst dequantized chroma transform coefficients and the seconddequantized chroma transform coefficient; add the chroma residual blockto a chroma prediction block to determine a decoded chroma block; andoutput decoded video data that includes the decoded chroma block.

According to another example of this disclosure, a device for decoding abitstream of encoded video data includes means for receiving, from thebitstream of encoded video data, a syntax element indicating whetherchroma scaling matrices are signaled for the encoded video data; meansfor determining a chroma scaling matrix for a block of the encoded videodata in response to determining that chroma scaling matrices aresignaled for the video data; means for determining a block of chromatransform coefficients for the block, wherein the block of chromatransform coefficients comprises at least a first chroma transformcoefficient and a second chroma transform coefficient; means fordetermining a quantization parameter (QP) value for the block of chromatransform coefficients; means for dequantizing the first chromatransform coefficient of the block of chroma transform coefficientsusing a first scaling value from the chroma scaling matrix and based onthe QP value; means for dequantizing the second chroma transformcoefficient of the block of chroma transform coefficients using a secondscaling value from the chroma scaling matrix and based on the QP value,wherein the second scaling value is different than the first scalingvalue; means for determining a chroma residual block for the block basedon the first dequantized chroma transform coefficients and the seconddequantized chroma transform coefficient; means for adding the chromaresidual block to a chroma prediction block to determine a decodedchroma block; and means for outputting decoded video data that includesthe decoded chroma block.

According to another example of this disclosure, a method of encodingvideo data includes in response to determining that a component of videodata is encoded in a mode where the component of video data isindependently decodable, setting a syntax element indicating whetherchroma scaling matrices are signaled for the video data to a valueindicating that the chroma scaling matrices are not signaled for thevideo data; and outputting in a bitstream of encoded video data, anindication of the value for the syntax element.

According to another example of this disclosure, a device for encodingvideo data includes a memory configured to store video data; one or moreprocessors implemented in circuitry and configured to: in response todetermining that a component of video data is encoded in a mode wherethe component of video data is independently decodable, set a syntaxelement indicating whether chroma scaling matrices are signaled for thevideo data to a value indicating that the chroma scaling matrices arenot signaled for the video data; and output in a bitstream of encodedvideo data, an indication of the value for the syntax element.

According to another example of this disclosure, a device for encodingvideo data includes means for setting a syntax element indicatingwhether chroma scaling matrices are signaled for the video data to avalue indicating that the chroma scaling matrices are not signaled forthe video data in response to determining that a component of video datais encoded in a mode where the component of video data is independentlydecodable; and means for outputting in a bitstream of encoded videodata, an indication of the value for the syntax element.

According to another example of this disclosure, a computer-readablestorage medium storing instructions that when executed by one or moreprocessors cause the one or more processors to: in response todetermining that a component of video data is encoded in a mode wherethe component of video data is independently decodable, set a syntaxelement indicating whether chroma scaling matrices are signaled for thevideo data to a value indicating that the chroma scaling matrices arenot signaled for the video data; and output in a bitstream of encodedvideo data, an indication of the value for the syntax element.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure, and a corresponding coding tree unit(CTU).

FIG. 3 is a block diagram illustrating an example video encoder that mayperform the techniques of this disclosure.

FIG. 4 is a block diagram illustrating an example video decoder that mayperform the techniques of this disclosure.

FIG. 5 is a flowchart illustrating an example process for videoencoding.

FIG. 6 is a flowchart illustrating an example process for videodecoding.

FIG. 7 is a flowchart illustrating an example process for videoencoding.

FIG. 8 is a flowchart illustrating an example process for videodecoding.

DETAILED DESCRIPTION

Video coding (e.g., video encoding and/or video decoding) typicallyinvolves predicting a block of video data from either an already codedblock of video data in the same picture (e.g., intra prediction) or analready coded block of video data in a different picture (e.g., interprediction). In some instances, the video encoder also calculatesresidual data by comparing the prediction block to the original block.Thus, the residual data represents a difference between the predictionblock and the original block. To reduce the number of bits needed tosignal the residual data, the video encoder transforms and quantizes theresidual data and signals the transformed and quantized residual data inthe encoded bitstream. A video encoder may uniformly quantize thetransformed residual data based on a value of a quantization parameter(QP). The video encoder may additionally or alternatively, perform afrequency-based quantization of the transformed residual data using aquantization matrix, also referred to as a scaling matrix, which resultsin different coefficients (associated with different frequencies) beingquantized differently. The compression achieved by the transform andquantization processes may be lossy, meaning that transform andquantization processes may introduce distortion into the decoded videodata.

A video decoder decodes and adds the residual data to the predictionblock to produce a reconstructed video block that matches the originalvideo block more closely than the prediction block alone. Due to theloss introduced by the transforming and quantizing of the residual data,the first reconstructed block may have distortion or artifacts. Onecommon type of artifact or distortion is referred to as blockingartifacts, where visible discontinuities across the boundaries of thecoding blocks is often observed primarily due to the different codingmethods of neighboring coding blocks.

To further improve the quality of decoded video, a video decoder canperform one or more filtering operations on the reconstructed videoblocks. Examples of these filtering operations include deblockingfiltering, sample adaptive offset (SAO) filtering, and adaptive loopfiltering (ALF). Parameters for these filtering operations may either bedetermined by a video encoder and explicitly signaled in the encodedvideo bitstream or may be implicitly determined by a video decoderwithout needing the parameters to be explicitly signaled in the encodedvideo bitstream.

As will be explained in more detail below, video data can include a lumacomponent and two chroma components. In some video bitstreams, thechroma components may be sub-sampled relative to the luma component, butin other instances, the chroma components may not be sub-sampled.Additionally, in some video bitstreams the decoding of chroma componentsmay be dependent on the luma components. That is, information associatedwith the luma component may be needed to decode the chroma components.Some video bitstreams may be coded using what is referred to as separatecolor plane coding, in which these dependencies are removed, making eachcomponent independently decodable. Separate color plane coding mayreduce compression, but may also reduce encoding and decoding latencydue to the fact that the different components may be decoded inparallel, which can be desirable for real-time applications such as livestreaming, video conferencing, and the like.

This disclosure describes techniques that may improve the signalingoverhead associated with encoding and decoding chroma components ofvideo data, and more specifically, may reduce the signaling overheadassociated with signaling chroma quantization matrices. The techniquesof this disclosure may be of particular value for video bitstreams thatutilize separate color plane coding or similar coding tools. Bysignaling a syntax element indicating whether chroma quantizationmatrices are signaled for the video data a video encoding and decodingsystem may reduce signal overhead by avoiding any unnecessary signalingof chroma quantization matrices, but at the same time, maintain theflexibility of enabling and disabling the use of chroma quantizationmatrices.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,unencoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1 , system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, mobile devices, tablet computers, set-top boxes,telephone handsets such as smartphones, televisions, cameras, displaydevices, digital media players, video gaming consoles, video streamingdevice, broadcast receiver devices, or the like. In some cases, sourcedevice 102 and destination device 116 may be equipped for wirelesscommunication, and thus may be referred to as wireless communicationdevices.

In the example of FIG. 1 , source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for usingquantization matrices for separate color plane coding. Thus, sourcedevice 102 represents an example of a video encoding device, whiledestination device 116 represents an example of a video decoding device.In other examples, a source device and a destination device may includeother components or arrangements. For example, source device 102 mayreceive video data from an external video source, such as an externalcamera. Likewise, destination device 116 may interface with an externaldisplay device, rather than include an integrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forusing quantization matrices for separate color plane coding. Sourcedevice 102 and destination device 116 are merely examples of such codingdevices in which source device 102 generates coded video data fortransmission to destination device 116. This disclosure refers to a“coding” device as a device that performs coding (encoding and/ordecoding) of data. Thus, video encoder 200 and video decoder 300represent examples of coding devices, in particular, a video encoder anda video decoder, respectively. In some examples, source device 102 anddestination device 116 may operate in a substantially symmetrical mannersuch that each of source device 102 and destination device 116 includesvideo encoding and decoding components. Hence, system 100 may supportone-way or two-way video transmission between source device 102 anddestination device 116, e.g., for video streaming, video playback, videobroadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e.,raw, unencoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some examples, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although memory 106 and memory 120 are shown separatelyfrom video encoder 200 and video decoder 300 in this example, it shouldbe understood that video encoder 200 and video decoder 300 may alsoinclude internal memories for functionally similar or equivalentpurposes. Furthermore, memories 106, 120 may store encoded video data,e.g., output from video encoder 200 and input to video decoder 300. Insome examples, portions of memories 106, 120 may be allocated as one ormore video buffers, e.g., to store raw, decoded, and/or encoded videodata.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may modulate a transmission signalincluding the encoded video data, and input interface 122 may demodulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video data generated by source device 102. Destinationdevice 116 may access stored video data from file server 114 viastreaming or download.

File server 114 may be any type of server device capable of storingencoded video data and transmitting that encoded video data to thedestination device 116. File server 114 may represent a web server(e.g., for a website), a server configured to provide a file transferprotocol service (such as File Transfer Protocol (FTP) or File Deliveryover Unidirectional Transport (FLUTE) protocol), a content deliverynetwork (CDN) device, a hypertext transfer protocol (HTTP) server, aMultimedia Broadcast Multicast Service (MBMS) or Enhanced MBMS (eMBMS)server, and/or a network attached storage (NAS) device. File server 114may, additionally or alternatively, implement one or more HTTP streamingprotocols, such as Dynamic Adaptive Streaming over HTTP (DASH), HTTPLive Streaming (HLS), Real Time Streaming Protocol (RTSP), HTTP DynamicStreaming, or the like.

Destination device 116 may access encoded video data from file server114 through any standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., digital subscriber line (DSL),cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on file server 114. Input interface122 may be configured to operate according to any one or more of thevarious protocols discussed above for retrieving or receiving media datafrom file server 114, or other such protocols for retrieving media data.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receivers, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., a communicationmedium, storage device 112, file server 114, or the like). The encodedvideo bitstream may include signaling information defined by videoencoder 200, which is also used by video decoder 300, such as syntaxelements having values that describe characteristics and/or processingof video blocks or other coded units (e.g., slices, pictures, groups ofpictures, sequences, or the like). Display device 118 displays decodedpictures of the decoded video data to a user. Display device 118 mayrepresent any of a variety of display devices such as a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device.

Although not shown in FIG. 1 , in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Alternatively, videoencoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as the Joint Exploration TestModel (JEM) or ITU-T H.266, also referred to as Versatile Video Coding(VVC). A recent draft of the VVC standard is described in Bross, et al.“Versatile Video Coding (Draft 7),” Joint Video Experts Team (WET) ofITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 16^(th) Meeting: Geneva,CH, 1-11 Oct. 2019, JVET-P2001-v14 (hereinafter “VVC Draft 7”). Adescription of the algorithms used in the VVC draft is described in J.Chen, Y. Ye, S. Kim, “Algorithm description for Versatile Video Codingand Test Model 7 (VTM7),” 16th JVET Meeting, Geneva, CH, October 2019,JVET-P2002. The techniques of this disclosure, however, are not limitedto any particular coding standard. Another draft of the VVC standard isdescribed in Bross, et al. “Versatile Video Coding (VVC Draft 10),”Joint Video Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC29/WG 11, 18^(th) Meeting: by teleconference, 22 Jun.-1 Jul. 2020,JVET-S2001-v17 (hereinafter “VVC Draft 10”). The techniques of thisdisclosure, however, are not limited to any particular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication. CTUs, CUs, PUs, and TUs may all generally bereferred to as “blocks” or “video blocks.”

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to VVC. According to VVC, a video coder(such as video encoder 200) partitions a picture into a plurality ofcoding tree units (CTUs). Video encoder 200 may partition a CTUaccording to a tree structure, such as a quadtree-binary tree (QTBT)structure or Multi-Type Tree (MTT) structure. The QTBT structure removesthe concepts of multiple partition types, such as the separation betweenCUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a firstlevel partitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using aquadtree (QT) partition, a binary tree (BT) partition, and one or moretypes of triple tree (TT) (also called ternary tree (TT)) partitions. Atriple or ternary tree partition is a partition where a block is splitinto three sub-blocks. In some examples, a triple or ternary treepartition divides a block into three sub-blocks without dividing theoriginal block through the center. The partitioning types in MTT (e.g.,QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT or MTT structure to represent each of the luminance andchrominance components, while in other examples, video encoder 200 andvideo decoder 300 may use two or more QTBT or MTT structures, such asone QTBT/MTT structure for the luminance component and another QTBT/MTTstructure for both chrominance components (or two QTBT/MTT structuresfor respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning, MTT partitioning, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

In some examples, a CTU includes a coding tree block (CTB) of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate color planes and syntaxstructures used to code the samples. A CTB may be an N×N block ofsamples for some value of N such that the division of a component intoCTBs is a partitioning. A component is an array or single sample fromone of the three arrays (luma and two chroma) that compose a picture in4:2:0, 4:2:2, or 4:4:4 color format or the array or a single sample ofthe array that compose a picture in monochrome format. In some examples,a coding block is an M×N block of samples for some values of M and Nsuch that a division of a CTB into coding blocks is a partitioning.

The blocks (e.g., CTUs or CUs) may be grouped in various ways in apicture. As one example, a brick may refer to a rectangular region ofCTU rows within a particular tile in a picture. A tile may be arectangular region of CTUs within a particular tile column and aparticular tile row in a picture. A tile column refers to a rectangularregion of CTUs having a height equal to the height of the picture and awidth specified by syntax elements (e.g., such as in a picture parameterset). A tile row refers to a rectangular region of CTUs having a heightspecified by syntax elements (e.g., such as in a picture parameter set)and a width equal to the width of the picture.

In some examples, a tile may be partitioned into multiple bricks, eachof which may include one or more CTU rows within the tile. A tile thatis not partitioned into multiple bricks may also be referred to as abrick. However, a brick that is a true subset of a tile may not bereferred to as a tile.

The bricks in a picture may also be arranged in a slice. A slice may bean integer number of bricks of a picture that may be exclusivelycontained in a single network abstraction layer (NAL) unit. In someexamples, a slice includes either a number of complete tiles or only aconsecutive sequence of complete bricks of one tile.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

Some examples of VVC also provide an affine motion compensation mode,which may be considered an inter-prediction mode. In affine motioncompensation mode, video encoder 200 may determine two or more motionvectors that represent non-translational motion, such as zoom in or out,rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. Some examples ofVVC provide sixty-seven intra-prediction modes, including variousdirectional modes, as well as planar mode and DC mode. In general, videoencoder 200 selects an intra-prediction mode that describes neighboringsamples to a current block (e.g., a block of a CU) from which to predictsamples of the current block. Such samples may generally be above, aboveand to the left, or to the left of the current block in the same pictureas the current block, assuming video encoder 200 codes CTUs and CUs inraster scan order (left to right, top to bottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT),an integer transform, a wavelet transform, or a conceptually similartransform to residual video data. Additionally, video encoder 200 mayapply a secondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the transform coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of the transformcoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) transform coefficients at the front of the vector and toplace lower energy (and therefore higher frequency) transformcoefficients at the back of the vector. In some examples, video encoder200 may utilize a predefined scan order to scan the quantized transformcoefficients to produce a serialized vector, and then entropy encode thequantized transform coefficients of the vector. In other examples, videoencoder 200 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form the one-dimensional vector, video encoder200 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as an adaptation parameter set (APS),sequence parameter set (SPS), picture parameter set (PPS), or videoparameter set (VPS). VVC Draft 7 defines a picture header as a syntaxstructure containing syntax elements that apply to all slices of a codedpicture. VVC Draft 7 defines an APS as a syntax structure containingsyntax elements that apply to zero or more slices as determined by zeroor more syntax elements found in slice headers. VVC Draft 7 defines aslice header as a part of a coded slice containing the data elementspertaining to all tiles or CTU rows within a tile represented in theslice. VVC Draft 7 defines a PPS as a syntax structure containing syntaxelements that apply to zero or more entire coded pictures as determinedby a syntax element found in each slice header. VVC Draft 7 defines anSPS syntax structure containing syntax elements that apply to zero ormore entire CLVSs as determined by the content of a syntax element foundin the PPS referred to by a syntax element found in each picture header.The VPS is the highest syntax structure, meaning the syntax elementsincluded in a VPS may apply to multiple SPSs. Video decoder 300 maylikewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information forpartitioning of a picture into CTUs, and partitioning of each CTUaccording to a corresponding partition structure, such as a QTBTstructure, to define CUs of the CTU. The syntax elements may furtherdefine prediction and residual information for blocks (e.g., CUs) ofvideo data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure 130, and a corresponding coding tree unit(CTU) 132. The solid lines represent quadtree splitting, and dottedlines indicate binary tree splitting. In each split (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting in this example.For the quadtree splitting, there is no need to indicate the splittingtype, because quadtree nodes split a block horizontally and verticallyinto 4 sub-blocks with equal size. Accordingly, video encoder 200 mayencode, and video decoder 300 may decode, syntax elements (such assplitting information) for a region tree level of QTBT structure 130(i.e., the solid lines) and syntax elements (such as splittinginformation) for a prediction tree level of QTBT structure 130 (i.e.,the dashed lines). Video encoder 200 may encode, and video decoder 300may decode, video data, such as prediction and transform data, for CUsrepresented by terminal leaf nodes of QTBT structure 130.

In general, CTU 132 of FIG. 2B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), then the nodes can befurther partitioned by respective binary trees. The binary treesplitting of one node can be iterated until the nodes resulting from thesplit reach the minimum allowed binary tree leaf node size (MinBTSize)or the maximum allowed binary tree depth (MaxBTDepth). The example ofQTBT structure 130 represents such nodes as having dashed lines forbranches. The binary tree leaf node is referred to as a coding unit(CU), which is used for prediction (e.g., intra-picture or inter-pictureprediction) and transform, without any further partitioning. Asdiscussed above, CUs may also be referred to as “video blocks” or“blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If thequadtree leaf node is 128×128, the leaf quadtree node will not befurther split by the binary tree, because the size exceeds the MaxBTSize(i.e., 64×64, in this example). Otherwise, the quadtree leaf node willbe further partitioned by the binary tree. Therefore, the quadtree leafnode is also the root node for the binary tree and has the binary treedepth as 0. When the binary tree depth reaches MaxBTDepth (4, in thisexample), no further splitting is permitted. A binary tree node having awidth equal to MinBTSize (4, in this example) implies that no furthervertical splitting (that is, dividing of the width) is permitted forthat binary tree node. Similarly, a binary tree node having a heightequal to MinBTSize implies no further horizontal splitting (that is,dividing of the height) is permitted for that binary tree node. As notedabove, leaf nodes of the binary tree are referred to as CUs, and arefurther processed according to prediction and transform without furtherpartitioning.

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If theleaf quadtree node is 128×128, the leaf quadtree node will not befurther split by the binary tree, because the size exceeds the MaxBTSize(i.e., 64×64, in this example). Otherwise, the leaf quadtree node willbe further partitioned by the binary tree. Therefore, the quadtree leafnode is also the root node for the binary tree and has the binary treedepth as 0. When the binary tree depth reaches MaxBTDepth (4, in thisexample), no further splitting is permitted. The binary tree node havinga width equal to MinBTSize (4, in this example) implies no furtherhorizontal splitting is permitted. Similarly, a binary tree node havinga height equal to MinBTSize implies no further vertical splitting ispermitted for that binary tree node. As noted above, leaf nodes of thebinary tree are referred to as CUs and are further processed accordingto prediction and transform without further partitioning.

Video encoder 200 and video decoder 300 may be configured to code videodata in various chroma formats. Video may be coded in a Y′CbCr colorspace (luma and chroma domain) as a color representation that is moresuitable for compression due to the decorrelating properties of thecolor space. Due to the sensitivities of the human visual system (HVS),the luma and the chroma components may be coded with different precisionor quality without significant effect on the perceived quality. In manyapplications, a reduction in quality is typically acceptable in order toalso reduce bandwidth and processing complexity. For example, in someapplications, chroma components may be coded with fewer bits or lesssamples without significantly affecting the quality. The advantage ofsuch differentiated coding is the reduced bitrate required to code thevideo.

One technique for reducing the number of chroma samples is to representthe chroma components (Cb and Cr) in a sub-sampled domain, also referredto as chroma sub-sampling. The particular sub-sampling format used forvideo may be signaled in the video. This indication may, for example, bereferred to as a chroma format indicator or idc. In VVC Draft 7, thechroma format indicator is signaled using the syntax elementchroma_format_idc. The table below shows the chroma format indicationsassociated with different values of chroma_format_idc:

Chroma subsampling format chroma_format_idc Description 4:4:4 3 Nochroma subsampling; for every sample of luma, there is one sample of Cband Cr component 4:2:2 2 The Cb and Cr components are subsampled (byfactor 2) in the horizontal direction. So for every two samples of luma,there is one sample each of Cb and Cr component. 4:2:0 1 The Cb and Crcomponents are subsampled (by factor 2) in the vertical and horizontaldirection. So for every four samples of luma, there is one sample eachof Cb and Cr component. 4:0:0 0 Chroma samples are not coded at all.Also called monochroma format.

For the sub-sampled 4:2:0 format and 4:2:2 format, different subsamplingfilters may result in different relative positions of the chromacomponents with respect to the luma component.

Video encoder 200 and video decoder 300 may be configured to performseparate color plane coding. In some instances, separate color planecoding may be limited to 4:4:4 formatted video. For content coded usingseparate color plane coding, video encoder 200 encodes the video suchthat there is no dependence between the coding of the three components,and thus, video decoder 300 can decode the three componentsindependently. In other words, the decoding or reconstruction of onecomponent does not depend on the decoding or reconstruction of anothercomponent. This coding mode may be limited to 4:4:4 formatted video andmay be indicated by a flag (e.g., separate_colour_plane_flag in VVCDraft 7) in a parameter set such as an SPS.

When the value of the syntax element separate_colour_plane_flag is equalto 1, video encoder 200 and video decoder 300 may encode and decode eachcomponent as though that component is a monochrome content withoutdependence on the other components. Even the chroma samples may be codedwith tools that are signaled or specified for luma samples. That is,each component may be encoded and decoded utilizing the same set ofcoding tools.

Video encoder 200 and video decoder 300 may be configured to utilizequantization matrices, also referred to as scaling matrices, whenquantizing transformed residual data. Scaling matrices are a set ofcoefficients that are used to scale the transform coefficients. Twoexample uses of scaling matrices are rate control and perceptualcontrol. Rate control for video is often performed by adjusting the QPvalues of blocks. However, the QP value results in a uniformquantization applied to all the frequency coefficients for a transformblock. Scaling matrices may be used for relative control between variouscoefficients within a transform block. For example, video encoder 200may define scaling matrices so that the low frequency coefficients arequantized less than the high frequency coefficients, which may bebeneficial for video where there is less high frequency content. Forperceptual control, scaling matrices may also be used to control therelative accuracy of coefficients within a transform block such thatperceptual quality of the video is maintained with lower bitrate.HVS-based quantization using scaling matrices can provide better qualityvideo for certain type of content (Refer: Sze, Budagavi and Sullivan,High Efficiency Video Coding (HEVC), Springer).

Video encoder 200 may signal the scaling matrices using scaling lists,which may be signaled as part of an APS. The scaling list may be enabledor disabled in the SPS, and if an SPS indicates that scaling lists areenabled, then there may be further control in the slice header to switchthe scaling matrices on and off for individual slices.

Scaling matrices may be defined for each transform block size. For aprediction type of the block, the matrices may be derived from scalinglists. The following syntax structure shows how scaling lists aresignaled in VVC Draft 7.

Descriptor scaling_list_data( ) { scaling_matrix_for_lfnst_disabled_flagu(1) for( id = 0; id < 28; id ++ ) matrixSize = (id < 2 ) ? 2 : ( ( id <8 ) ? 4 : 8 ) scaling_list_copy_mode_flag[ id ] u(1) if(!scaling_list_copy_mode_flag[ id ] ) scaling_list_pred_mode_flag[ id ]u(1) if( ( scaling_list_copy_mode_flag[ id ] | |scaling_list_pred_mode_flag [ id ] ) && id != 0 && id != 2 && id != 8 )scaling_list_pred_id_delta[ id ] ue(v) if( !scaling_list_copy_mode_flag[id ] ) { nextCoef = 0 if( id > 13 ) { scaling_list_dc_coef[ id − 14 ]se(v) nextCoef += scaling_list_dc_coef[ id − 14 ] } for( i = 0; i <matrixSize * matrixSize; i++ ) { x = DiagScanOrder[ 3 ][ 3 ][ i ][ 0 ] y= DiagScanOrder[ 3 ][ 3 ][ i ][ 1 ] if( !( id > 25 && x >= 4 && y >= 4 )) { scaling_list_delta_coef[ id ][ i ] se(v) nextCoef +=scaling_list_delta_coef[ id ][ i ] } ScalingList[ id ][ i ] = nextCoef }} } }

The correspondence of the scaling lists (with ID 0 to 27) and theparticular components are provided in the following table (Table 36 inVVC Draft 7)

max(nTbW, nTbH) 2 4 8 16 32 64 predMode = cIdx = 0 (Y) 2 8 14 20 26MODE_INTRA cIdx = 1 (Cb) 3 9 15 21 21 cIdx = 2 (Cr) 4 10 16 22 22predMode = cIdx = 0 (Y) 5 11 17 23 27 MODE_INTER cIdx = 1 (Cb) 0 6 12 1824 24 (INTER, IBC) cIdx = 2 (Cr) 1 7 13 19 25 25

Three arrays are defined representing the scaling list IDs of eachcomponent as follows:

ScalingListIdsY={2, 5, 8, 11, 14, 17, 20, 23, 26, 27}

ScalingListIdsCb={0, 3, 6, 9, 12, 15, 18, 21, 24}

ScalingListIdsCr={1, 4, 7, 10, 13, 16, 19, 22, 25}

A function IsIdInList(id, scalingList) is defined such that when thevalue of id is present in the list scalingList, the function returns thevalue true, otherwise the function returns the value false. For example,IsIdInList(14, ScalingListIdsY) will return true, whereas IsIdInList(15,ScalingListIDsCr) will return false.

For other implementations, the arrays above may be initialized accordingto the IDs associated with each component.

Existing techniques for utilizing quantization matrices may have someproblems. For example, in VVC Draft 7, the quantization matrices aresignaled for luma and chroma components irrespective of the chromasampling format used. In some cases, the chroma format indicator may besignaled to have a value of 0 (i.e., 4:0:0 format) when the content iscoded in monochrome format, as described in H. Zhang, X. Li, G. Li, L.Li, S. Liu, “AHG15: Improvement for Quantization MatrixSignalling,”17^(th) JVET Meeting, Brussels, BE, January 2019,JVET-Q0505. In such cases, the quantization matrices corresponding tochroma components may not be signaled. However, when thechroma_format_idc is equal to 3 (i.e., 4:4:4 format) and the video iscoded as separate color plane coding, the quantization matrices aresignaled for the chroma components, even though the quantizationmatrices may not be used, resulting in unnecessary bits to be signaled.

This disclosure describes techniques that may address these problems.The various techniques described herein may be performed by videoencoder 200 and video decoder 300 independently or may be applied incombination with one or more other techniques described herein.

In one example technique, video encoder 200 and video decoder 300 may beconfigured to process a syntax element signaled to indicate whetherscaling lists are signaled for one component or all three components.When the scaling list is only signaled for one component, the scalinglist may apply to all three components.

In one example technique, video encoder 200 and video decoder 300 may beconfigured to process a first syntax element to determine the presenceof chroma quantization matrices. The first syntax element may beindicative that the video is coded as separate color planes. In suchcases, the first syntax element may be constrained to be equal toseparate_colour_plane_flag signalled in the SPS or other parts of thebitstream. The first syntax element may indicate a number of componentsfor which the quantization matrices are signaled; e.g., when the firstsyntax element is equal to 1, quantization matrices for only onecomponent may be signaled and may apply to the luma samples; when thefirst syntax element is equal to 3, the three QMs may apply to the threecomponents Y, Cb, and Cr. In some examples, the first syntax element maybe constrained to not be equal to 0. In some examples, the first syntaxmay be signaled as a “minus1” value such that it is not possible tosignal a value for the first syntax element.

In another example technique, video encoder 200 and video decoder 300may be configured to derive a first variable from the first syntaxelement to specify whether the chroma quantization matrices aresignaled. As one example, when the first syntax element indicates aseparate color plane coding is employed: the first variable may bederived to be 0 indicating that the chroma quantization matrices are notsignaled, otherwise the first variable may be set to 1. As anotherexample, when the first syntax element is a number of components forwhich the QM are signaled: the first variable may be derived to be 0when number of components is indicates one component; otherwise thefirst variable may be set to 1. In some examples, the first variable maybe derived separately for Cb and Cr components.

In another example technique, video encoder 200 may refrain fromsignaling explicit chroma quantization matrices in the bitstream basedon a value of the first variable that specifies that the chromaquantization matrices are not signaled.

In another example technique, based on the absence of explicit chromaquantization matrices, video encoder 200 and video decoder 300 maydetermine whether to apply the luma quantization matrices, whenavailable, also to the chroma components or refrain from applying QMscaling to chroma components.

In some examples, video encoder 200 and video decoder 300 may process aflag signaled to indicate whether one or three scaling lists aresignaled. When a scaling list for one component is signaled, that listapplies to the luma component when separate color plane coding isdisabled or applies to all three components when separate color planecoding is enabled. In the table below, added text is shown in betweenthe symbols <add> and </add>.

Descriptor scaling_list_data( ) { scaling_matrix_for_lfnst_disabled_flagu(1) <add>scaling_matrix_separate_plane_processing_flag</add> <add>u(2)</add> for( id = 0; id < 28; id ++ ) {<add>if(scaling_matrix_separate_plane_processing_flag = = 0 ||(scaling_matrix_separate_plane_processing_flag != 0 && !( IsIdInList(id, ScalingListIdsCb) || IsIdInList( id, ScalingListIdsCr) ) ) ) </add>matrixSize = (id < 2 ) ? 2 : ( ( id < 8 ) ? 4 : 8 )scaling_list_copy_mode_flag[ id ] u(1) if( !scaling_list_copy_mode_flag[id ] ) scaling_list_pred_mode_flag[ id ] u(1) if( (scaling_list_copy_mode_flag[ id ] | | scaling_list_pred_mode_flag [ id ]) && id != 0 && id != 2 && id != 8 ) scaling_list_pred_id_delta[ id ]ue(v) if( !scaling_list_copy_mode_flag[ id ] ) { nextCoef = 0 if( id >13 ) { scaling_list_dc_coef[ id − 14 ] se(v) nextCoef +=scaling_list_dc_coef[ id − 14 ] } for( i = 0; i < matrixSize *matrixSize; i++ ) { x = DiagScanOrder[ 3 ][ 3 ][ i ][ 0 ] y =DiagScanOrder[ 3 ][ 3 ][ i ][ 1 ] if( !( id > 25 && x >= 4 && y >= 4 ) ){ scaling_list_delta_coef[ id ][ i ] se(v) nextCoef +=scaling_list_delta_coef[ id ][ i ] } ScalingList[ id ][ i ] = nextCoef }} } } }

The syntax element scaling_matrix_separate_plane_processing_flag equalto 0 specifies that scaling matrices for all three components aresignaled in the APS. scaling_matrix_separate_plane_processing_flag equalto 1 specifies that the scaling matrix is only specified for onecomponent.

In some examples, video encoder 200 may be configured to encode videodata in accordance with the following example constraints.

-   -   In one example, the following constraint may be added:

It is requirement of bitstream conformance thatscaling_matrix_separate_plane_processing_flag shall not be equal to 1only when separate_colour_plane_coding_flag is equal to 0.

-   -   In another example, the following constraint may be added:

It is requirement of bitstream conformance thatscaling_matrix_separate_plane_processing_flag shall be equal toseparate_colour_plane_coding_flag ? 1:(chroma_format_idc ? 0:1).

-   -   In another example, the following constraint may be added:

When separate_colour_plane_flag is equal to 1 andscaling_matrix_separate_plane_processing_flag is equal to 1, the scalinglist signaled for the luma component also applies to the Cb and Crcomponents.

In some examples, video encoder 200 and video decoder 300 may beconfigured to process chroma format idc and separate color plane codinginformation signaled in the scaling list APS, and depending on the valueof chroma format idc and separate color plane coding, some quantizationmatrices may not be signaled. In the table below, added text is shown inbetween the symbols <add> and </add>.

Descriptor scaling_list_data( ) { scaling_matrix_for_lfnst_disabled_flagu(1) <add>scaling_matrix_chroma_format_idc</add> <add>u(2) </add><add>scaling_matrix_separate_colour_plane_flag</add> <add>u(1) </add>for( id = 0; id < 28; id ++ ) { <add>if( SMChromaFormatIdc != 0 || (SMChromaFormatIdc = = 0 && !( IsIdInList( id, ScalingListIdsCb) ||IsIdInList( id, ScalingListIdsCr) ) ) ) </add> matrixSize = (id < 2 ) ?2 : ( ( id < 8 ) ? 4 : 8 ) scaling_list_copy_mode_flag[ id ] u(1) if(!scaling_list_copy_mode_flag[ id ] ) scaling_list_pred_mode_flag[ id ]u(1) if( ( scaling_list_copy_mode_flag[ id ] | |scaling_list_pred_mode_flag [ id ] ) && id != 0 && id != 2 && id != 8 )scaling_list_pred_id_delta[ id ] ue(v) if( !scaling_list_copy_mode_flag[id ] ) { nextCoef = 0 if( id > 13 ) { scaling_list_dc_coef[ id − 14 ]se(v) nextCoef += scaling_list_dc_coef[ id − 14 ] } for( i = 0; i <matrixSize * matrixSize; i++ ) { x = DiagScanOrder[ 3 ][ 3 ][ i ][ 0 ] y= DiagScanOrder[ 3 ][ 3 ][ i ][ 1 ] if( !( id > 25 && x >= 4 && y >= 4 )) { scaling_list_delta_coef[ id ][ i ] se(v) nextCoef +=scaling_list_delta_coef[ id ][ i ] } ScalingList[ id ][ i ] = nextCoef }} } } }

The semantics of scaling_matrix_chroma_format_idc andscaling_matrix_separate_colour_plane_flag are similar to the semanticsof chroma_format_idc and separate_colour_plane_flag, respectively. Thevalues of scaling_matrix_chroma_format_idc andscaling_matrix_separate_colour_plane_flag may also be constrained to beequal to the values of chroma_format_idc and separate_colour_plane_flag,respectively.

The variable ChromaFormatIdc may be derived as follows:SMChromaFormatIdc=scaling_matrix_separate_colour_plane_flag?0:scaling_matrix_chroma_format_idc

In some examples, the syntax element scaling_matrix_chroma_format_idcand scaling_matrix_separate_colour_plane_flag is not signalled andinstead a syntax element that signals the value equivalent toSMChromaFormatIdc is signaled and the determination of signaling chromaQM is based on that syntax element.

In some examples, a number of components for which the QMs are signaledis included in the syntax element. In the table below, added text isshown in between the symbols <add> and </add>.

Descriptor scaling_list_data( ) { scaling_matrix_for_lfnst_disabled_flagu(1) <add> scaling_matrix_num_component_minus1s</add> <add> ue(v) </add>for( id = 0; id < 28; id ++ ) { <add> if( SMNumComps = = 3 || (SMNumComps = = 2 && ! IsIdInList( id, ScalingListIdsCr) ) || (SMNumComps = = 1 && !( IsIdInList( id, ScalingListIdsCb) || IsIdInList(id, ScalingListIdsCr) ) ) ) </add> matrixSize = (id < 2 ) ? 2 : ( ( id <8 ) ? 4 : 8 ) scaling_list_copy_mode_flag[ id ] u(1) if(!scaling_list_copy_mode_flag[ id ] ) scaling_list_pred_mode_flag[ id ]u(1) if( ( scaling_list_copy_mode_flag[ id ] | |scaling_list_pred_mode_flag [ id ] ) && id != 0 && id != 2 && id != 8 )scaling_list_pred_id_delta[ id ] ue(v) if( !scaling_list_copy_mode_flag[id ] ) { nextCoef = 0 if( id > 13 ) { scaling_list_dc_coef[ id − 14 ]se(v) nextCoef += scaling_list_dc_coef[ id − 14 ] } for( i = 0; i <matrixSize * matrixSize; i++ ) { x = DiagScanOrder[ 3 ][ 3 ][ i ][ 0 ] y= DiagScanOrder[ 3 ][ 3 ][ i ][ 1 ] if( !( id > 25 && x >= 4 && y >= 4 )) { scaling_list_delta_coef[ id ][ i ] se(v) nextCoef +=scaling_list_delta_coef[ id ][ i ] } ScalingList[ id ][ i ] = nextCoef }} } } }

The syntax element scaling_matrix_num_components_minus1 plus 1 specifiesthe number of components for which the scaling lists are signaled. Thevalue of scaling_matrix_num_components_minus1 shall be in the range of 0to 2, inclusive.

The value of SMNumComps is set qual toscaling_matrix_num_components_minus1+1.

The scaling lists for components for which the scaling lists are notspecified may use the scaling list associated with the first component,e.g. luma component.

In some examples, when scaling lists are signaled for 2 components, thefirst component scaling lists may apply to luma and the second componentscaling lists may apply to both luma and chroma.

In some examples, for each component comp for which QMs are not signaledbased on scaling_matrix_num_components_minus1, a further syntax elementmay be signaled to indicate whether:

-   -   The QM is disabled for component comp    -   The ID of the component whose QM is to be used for component        comp. For example, if only two components are signaled, then the        for the Cr component, an id may specify whether the scaling list        associated with luma or the scaling list associated with chroma        is to be applied to the Cr component.

FIG. 3 is a block diagram illustrating an example video encoder 200 thatmay perform the techniques of this disclosure. FIG. 3 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200according to the techniques of JEM, VVC (ITU-T H.266, underdevelopment), and HEVC (ITU-T H.265). However, the techniques of thisdisclosure may be performed by video encoding devices that areconfigured to other video coding standards.

In the example of FIG. 3 , video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videoencoder 200 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video encoder 200 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1 ). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 3 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, one or more of the units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1 ) may storethe instructions (e.g., object code) of the software that video encoder200 receives and executes, or another memory within video encoder 200(not shown) may store such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,unencoded version of the current block from video data memory 230 andthe prediction block from mode selection unit 202. Residual generationunit 204 calculates sample-by-sample differences between the currentblock and the prediction block. The resulting sample-by-sampledifferences define a residual block for the current block. In someexamples, residual generation unit 204 may also determine differencesbetween sample values in the residual block to generate a residual blockusing residual differential pulse code modulation (RDPCM). In someexamples, residual generation unit 204 may be formed using one or moresubtractor circuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder200 and video decoder 300 may also support asymmetric partitioning forPU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit 202 does not further partition aCU into PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as fewexamples, mode selection unit 202, via respective units associated withthe coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block aswell as using scaling matrices as described above. Video encoder 200(e.g., via mode selection unit 202) may adjust the degree ofquantization applied to the transform coefficient blocks associated withthe current block by adjusting the QP value associated with the CU.Quantization may introduce loss of information, and thus, quantizedtransform coefficients may have lower precision than the originaltransform coefficients produced by transform processing unit 206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from theprediction block generated by mode selection unit 202 to produce thereconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not needed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are needed, filter unit 216may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying a MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding block andthe chroma coding blocks.

Video encoder 200 represents an example of a device configured to encodevideo data and that includes a memory configured to store video data,and one or more processing units implemented in circuitry and configuredto perform the techniques of this disclosure, including the techniquesdescribed below in the claims section.

FIG. 4 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 4 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 according tothe techniques of JEM, VVC (ITU-T H.266, under development), and HEVC(ITU-T H.265). However, the techniques of this disclosure may beperformed by video coding devices that are configured to other videocoding standards.

In the example of FIG. 4 , video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videodecoder 300 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video decoder 300 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeadditional units to perform prediction in accordance with otherprediction modes. As examples, prediction processing unit 304 mayinclude a palette unit, an intra-block copy unit (which may form part ofmotion compensation unit 316), an affine unit, a linear model (LM) unit,or the like. In other examples, video decoder 300 may include more,fewer, or different functional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1 ). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as DRAM, including SDRAM, MRAM,RRAM, or other types of memory devices. CPB memory 320 and DPB 314 maybe provided by the same memory device or separate memory devices. Invarious examples, CPB memory 320 may be on-chip with other components ofvideo decoder 300, or off-chip relative to those components.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1 ). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 4 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 3 , fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, one or moreof the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, one or more of the units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP and the scaling matrices associated with thequantized transform coefficient block to determine a degree ofquantization and, likewise, a degree of inverse quantization for inversequantization unit 306 to apply. Inverse quantization unit 306 may, forexample, perform a bitwise left-shift operation to inverse quantize thequantized transform coefficients. Inverse quantization unit 306 maythereby form a transform coefficient block including transformcoefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the transform coefficient block.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 3 ).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 3 ).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Forinstance, in examples where operations of filter unit 312 are notperformed, reconstruction unit 310 may store reconstructed blocks to DPB314. In examples where operations of filter unit 312 are performed,filter unit 312 may store the filtered reconstructed blocks to DPB 314.As discussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures (e.g.,decoded video) from DPB 314 for subsequent presentation on a displaydevice, such as display device 118 of FIG. 1 .

Video decoder 300 represents an example of a device configured to decodevideo data and that includes a memory configured to store video data andone or more processing units implemented in circuitry and configured toperform the techniques of this disclosure, including the techniquesdescribed below in the claims section.

FIG. 5 is a flowchart illustrating an example method for encoding acurrent block. The current block may comprise a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 3 ), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 5 .

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. Video encoder 200 may then calculate a residual blockfor the current block (352). To calculate the residual block, videoencoder 200 may calculate a difference between the original, unencodedblock and the prediction block for the current block. Video encoder 200may then transform the residual block and quantize transformcoefficients of the residual block (354). Next, video encoder 200 mayscan the quantized transform coefficients of the residual block (356).During the scan, or following the scan, video encoder 200 may entropyencode the transform coefficients (358). For example, video encoder 200may encode the transform coefficients using CAVLC or CABAC. Videoencoder 200 may then output the entropy encoded data of the block (360).

FIG. 6 is a flowchart illustrating an example method for decoding acurrent block of video data. The current block may comprise a currentCU. Although described with respect to video decoder 300 (FIGS. 1 and 4), it should be understood that other devices may be configured toperform a method similar to that of FIG. 6 .

Video decoder 300 may receive entropy encoded data for the currentblock, such as entropy encoded prediction information and entropyencoded data for coefficients of a residual block corresponding to thecurrent block (370). Video decoder 300 may entropy decode the entropyencoded data to determine prediction information for the current blockand to reproduce coefficients of the residual block (372). Video decoder300 may predict the current block (374), e.g., using an intra- orinter-prediction mode as indicated by the prediction information for thecurrent block, to calculate a prediction block for the current block.Video decoder 300 may then inverse scan the reproduced coefficients(376), to create a block of quantized transform coefficients. Videodecoder 300 may then inverse quantize and inverse transform thetransform coefficients to produce a residual block (378). Video decoder300 may ultimately decode the current block by combining the predictionblock and the residual block (380).

FIG. 7 is a flowchart illustrating an example method for encoding videodata. Although described with respect to video encoder 200 (FIGS. 1 and3 ), it should be understood that other devices may be configured toperform a method similar to that of FIG. 7 .

In response to determining that a component of video data is encoded ina mode where the component of video data is independently decodable,video encoder 200 sets a syntax element indicating whether chromascaling matrices are signaled for the video data to a value indicatingthat the chroma scaling matrices are not signaled for the video data(390). Video encoder 200 outputs in a bitstream of encoded video data,an indication of the value for the syntax element (392). To determinethat the component of video data is encoded in the mode where thecomponent of video data is independently decodable, video encoder 200may be configured to determine that the video data is encoded in aseparate color plane coding mode. The video data may include 4:4:4 videodata.

FIG. 8 is a flowchart illustrating an example method for decoding acurrent block of video data. The current block may comprise a currentCU. Although described with respect to video decoder 300 (FIGS. 1 and 4), it should be understood that other devices may be configured toperform a method similar to that of FIG. 8 .

Video decoder 300 receives a syntax element indicating whether chromaquantization matrices are signaled for the video data (400). In responseto determining that chroma quantization matrices are signaled for thevideo data, video decoder 300 determines a chroma quantization matrixfor a block of video data (402). Video decoder 300 determines a block ofchroma transform coefficients for the block of video data (404). Videodecoder 300 dequantizes a first chroma transform coefficient of theblock of chroma transform coefficients using a first quantization valuefrom the chroma quantization matrix (406). Video decoder 300 dequantizesa second chroma transform coefficient of the block of chroma transformcoefficients using a second quantization value from the chromaquantization matrix (408). Video decoder 300 determines a chromaresidual block for the block of video data based on the firstdequantized chroma transform coefficients and the second dequantizedchroma transform coefficient (410). Video decoder 300 adds the chromaresidual block to a chroma prediction block to determine a decodedchroma block (412). Video decoder 300 outputs decoded video data thatincludes the decoded chroma block (414).

The following clauses describe aspects of techniques and devicesintroduced above.

Clause 1: A method of decoding video data includes receiving a syntaxelement indicating whether scaling lists are signaled for one componentof the video data; determining the scaling lists; and decoding the videodata based on the determined scaling lists.

Clause 2: The method of clause 1, further includes determining whetherseparate color plane coding is enabled.

Clause 3: The method of clause 2, further includes in response todetermining that color plane coding enabled, using the scaling lists todecode a luma component of the video data, a first chroma component ofthe video data, and a second chroma component of the video data.

Clause 4: The method of clause 2, further includes in response todetermining that color plane coding disabled, using the scaling lists todecode a luma component of the video data.

Clause 5: The method of clause 2, further includes in response todetermining that color plane coding disabled, using the scaling lists todecode a luma component of the video data without using the scalinglists to decode a first chroma component of the video data or a secondchroma component of the video data.

Clause 6: A method of decoding video data includes receiving a syntaxelement indicating whether chroma quantization matrices are signaled forthe video data; determining the chroma quantization matrices; anddecoding the video data based on the determined chroma quantizationmatrices.

Clause 7: The method of clause 6, wherein the syntax element indicates anumber of components for which the chroma quantization matrices aresignaled

Clause 8: The method of clause 6, further includes deriving a firstvariable from the syntax element; and based on the derived firstvariable, determining whether the chroma quantization matrices aresignaled.

Clause 9: A device for coding video data, the device comprising one ormore means for performing the method of any of clauses 1-8.

Clause 10: The device of clause 9, wherein the one or more meanscomprise one or more processors implemented in circuitry.

Clause 11: The device of any of clauses 9 and 10, further comprising amemory to store the video data.

Clause 12: The device of any of clauses 9-11, further comprising adisplay configured to display decoded video data.

Clause 13: The device of any of clauses 9-12, wherein the devicecomprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.

Clause 14: The device of any of clauses 9-13, wherein the devicecomprises a video decoder.

Clause 15: A computer-readable storage medium having stored thereoninstructions that, when executed, cause one or more processors toperform the method of any of clauses 1-8.

Clause 16: A method of decoding a bitstream of encoded video data, themethod comprising receiving, from the bitstream of encoded video data, asyntax element indicating whether chroma scaling matrices are signaledfor the encoded video data; in response to determining that chromascaling matrices are signaled for the video data, determining a chromascaling matrix for a block of the encoded video data; determining ablock of chroma transform coefficients for the block, wherein the blockof chroma transform coefficients comprises at least a first chromatransform coefficient and a second chroma transform coefficient;determining a quantization parameter (QP) value for the block of chromatransform coefficients; dequantizing the first chroma transformcoefficient of the block of chroma transform coefficients using a firstscaling value from the chroma scaling matrix and based on the QP value;dequantizing the second chroma transform coefficient of the block ofchroma transform coefficients using a second scaling value from thechroma scaling matrix and based on the QP value, wherein the secondscaling value is different than the first scaling value; determining achroma residual block for the block based on the first dequantizedchroma transform coefficients and the second dequantized chromatransform coefficient; adding the chroma residual block to a chromaprediction block to determine a decoded chroma block; and outputtingdecoded video data that includes the decoded chroma block.

Clause 17: The method of clause 16, wherein determining the chromascaling matrix for the block of video data comprises receiving thechroma scaling matrix in a parameter set syntax structure.

Clause 18: The method of clause 17, wherein the parameter set syntaxstructure comprises an adaptation parameter set syntax structure.

Clause 19: The method of any of clauses 16-18, further comprising addingthe chroma residual block to the chroma prediction block to determine areconstructed chroma block; and applying one or more filters to thereconstructed chroma block to determine the decoded chroma block.

Clause 20: The method of any of clauses 16-19, wherein the block ofvideo data comprises a 4:4:4 block of video data.

Clause 21: The method of any of clauses 16-20, wherein the block ofvideo data is coded in a separate color plane coding mode.

Clause 22: The method of any of clauses 16-21, further comprisingselecting the first scaling value based on a frequency of the firstchroma transform coefficient; and selecting the second scaling valuebased on a frequency of the second chroma transform coefficient.

Clause 23: The method of any of clauses 16-22, wherein the video datacomprises first video data associated with a first parameter set, themethod further comprising: receiving a second syntax element indicatingwhether second chroma scaling matrices are signaled for second videodata associated with a second parameter set; in response to determiningthat the second chroma scaling matrices are not signaled for the secondvideo data, determining a luma scaling matrix for a block of the secondvideo data without receiving a corresponding chroma scaling matrix.

Clause 24: The method of any of clauses 16-23, further comprising:determining a luma scaling matrix for the block of video data;determining a block of luma transform coefficients for the block ofvideo data, wherein the block of luma transform coefficients comprisesat least a first luma transform coefficient and a second luma transformcoefficient; determining a second quantization parameter (QP) value forthe block of luma transform coefficients; dequantizing the first lumatransform coefficient of the block of luma transform coefficients usinga first scaling value from the luma scaling matrix and based on thesecond QP value; dequantizing the second luma transform coefficient ofthe block of luma transform coefficients using a second scaling valuefrom the luma quantization matrix and based on the second QP value;determining a luma residual block for the block of video data based onthe first dequantized luma transform coefficients and the seconddequantized luma transform coefficient; adding the luma residual blockto a luma prediction block to determine a decoded luma block, whereinthe decoded video data includes the decoded luma block.

Clause 25: A device for decoding video data, the device comprising: amemory configured to store video data and one or more processorsimplemented in circuitry and configured to: receive, from the bitstreamof encoded video data, a syntax element indicating whether chromascaling matrices are signaled for the encoded video data; in response todetermining that chroma scaling matrices are signaled for the videodata, determine a chroma scaling matrix for a block of the encoded videodata; determine a block of chroma transform coefficients for the block,wherein the block of chroma transform coefficients comprises at least afirst chroma transform coefficient and a second chroma transformcoefficient; determine a quantization parameter (QP) value for the blockof chroma transform coefficients; dequantize the first chroma transformcoefficient of the block of chroma transform coefficients using a firstscaling value from the chroma scaling matrix and based on the QP value;dequantize the second chroma transform coefficient of the block ofchroma transform coefficients using a second scaling value from thechroma scaling matrix and based on the QP value, wherein the secondscaling value is different than the first scaling value; determine achroma residual block for the block based on the first dequantizedchroma transform coefficients and the second dequantized chromatransform coefficient; add the chroma residual block to a chromaprediction block to determine a decoded chroma block; and output decodedvideo data that includes the decoded chroma block.

Clause 26: The device of clause 25, wherein to determine the chromascaling matrix for the block of video data, the one or more processorsare further configured to receive the chroma scaling matrix in aparameter set syntax structure.

Clause 27: The device of clause 26, wherein the parameter set syntaxstructure comprises an adaptation parameter set syntax structure.

Clause 28: The device of any of clauses 25-27, wherein the one or moreprocessors are further configured to: add the chroma residual block tothe chroma prediction block to determine a reconstructed chroma block;and apply one or more filters to the reconstructed chroma block todetermine the decoded chroma block.

Clause 29: The device of any of clauses 25-28, wherein the block ofvideo data comprises a 4:4:4 block of video data.

Clause 30: The device of any of clauses 25-29, wherein the block ofvideo data is coded in a separate color plane coding mode.

Clause 31: The device of any of clauses 25-30, wherein the one or moreprocessors are further configured to: select the first scaling valuebased on a frequency of the first chroma transform coefficient; andselect the second scaling value based on a frequency of the secondchroma transform coefficient.

Clause 32: The device of any of clauses 25-31, wherein the video datacomprises first video data associated with a first parameter set,wherein the one or more processors are further configured to: receive asecond syntax element indicating whether second chroma scaling matricesare signaled for second video data associated with a second parameterset; in response to determining that the second chroma scaling matricesare not signaled for the second video data, determine a luma scalingmatrix for a block of the second video data without receiving acorresponding chroma scaling matrix.

Clause 33: The device of any of clauses 25-32, wherein the one or moreprocessors are further configured to: determine a luma scaling matrixfor the block of video data; determine a block of luma transformcoefficients for the block of video data, wherein the block of lumatransform coefficients comprises at least a first luma transformcoefficient and a second luma transform coefficient; determine a secondquantization parameter (QP) value for the block of luma transformcoefficients; dequantize the first luma transform coefficient of theblock of luma transform coefficients using a first scaling value fromthe luma scaling matrix and based on the second QP value; dequantize thesecond luma transform coefficient of the block of luma transformcoefficients using a second scaling value from the luma quantizationmatrix and based on the second QP value; determine a luma residual blockfor the block of video data based on the first dequantized lumatransform coefficients and the second dequantized luma transformcoefficient; and add the luma residual block to a luma prediction blockto determine a decoded luma block, wherein the decoded video dataincludes the decoded luma block.

Clause 34: The device of any of clauses 25-33, wherein the devicecomprises a wireless communication device, further comprising a receiverconfigured to receive encoded video data.

Clause 35: The device of clause 34, wherein the wireless communicationdevice comprises a telephone handset and wherein the receiver isconfigured to demodulate, according to a wireless communicationstandard, a signal comprising the encoded video data.

Clause 36: The device of any of clauses 25-35, further comprising: adisplay configured to display decoded video data.

Clause 37: The device of any of clauses 25-36, wherein the devicecomprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.

Clause 38: A computer-readable storage medium storing instructions thatwhen executed by one or more processors cause the one or more processorsto: receive, from a bitstream of encoded video data, a syntax elementindicating whether chroma scaling matrices are signaled for the encodedvideo data; in response to determining that chroma scaling matrices aresignaled for the video data, determine a chroma scaling matrix for ablock of the encoded video data; determine a block of chroma transformcoefficients for the block, wherein the block of chroma transformcoefficients comprises at least a first chroma transform coefficient anda second chroma transform coefficient; determine a quantizationparameter (QP) value for the block of chroma transform coefficients;dequantize the first chroma transform coefficient of the block of chromatransform coefficients using a first scaling value from the chromascaling matrix and based on the QP value; dequantize the second chromatransform coefficient of the block of chroma transform coefficientsusing a second scaling value from the chroma scaling matrix and based onthe QP value, wherein the second scaling value is different than thefirst scaling value; determine a chroma residual block for the blockbased on the first dequantized chroma transform coefficients and thesecond dequantized chroma transform coefficient; add the chroma residualblock to a chroma prediction block to determine a decoded chroma block;and output decoded video data that includes the decoded chroma block.

Clause 39: The computer-readable storage medium of clause 38, wherein todetermine the chroma scaling matrix for the block of video data, theinstructions are configured to cause the one or more processors toreceive the chroma scaling matrix in a parameter set syntax structure.

Clause 40: The computer-readable storage medium of clause 39, whereinthe parameter set syntax structure comprises an adaptation parameter setsyntax structure.

Clause 41: The computer-readable storage medium of any of clauses 38-40,wherein the one or more processors are further configured to: add thechroma residual block to the chroma prediction block to determine areconstructed chroma block; and apply one or more filters to thereconstructed chroma block to determine the decoded chroma block.

Clause 42: The computer-readable storage medium of any of clauses 38-41,wherein the block of video data comprises a 4:4:4 block of video data.

Clause 43: The computer-readable storage medium of any of clauses 38-42,wherein the block of video data is coded in a separate color planecoding mode.

Clause 44: The computer-readable storage medium of any of clauses 38-43,wherein the one or more processors are further configured to: select thefirst scaling value based on a frequency of the first chroma transformcoefficient; and select the second scaling value based on a frequency ofthe second chroma transform coefficient.

Clause 45: The computer-readable storage medium of any of clauses 38-44,wherein the video data comprises first video data associated with afirst parameter set, wherein the one or more processors are furtherconfigured to: receive a second syntax element indicating whether secondchroma scaling matrices are signaled for second video data associatedwith a second parameter set; in response to determining that the secondchroma scaling matrices are not signaled for the second video data,determine a luma scaling matrix for a block of the second video datawithout receiving a corresponding chroma scaling matrix.

Clause 46: The computer-readable storage medium of any of clauses 38-45,wherein the one or more processors are further configured to: determinea luma scaling matrix for the block of video data; determine a block ofluma transform coefficients for the block of video data, wherein theblock of luma transform coefficients comprises at least a first lumatransform coefficient and a second luma transform coefficient; determinea second quantization parameter (QP) value for the block of lumatransform coefficients; dequantize the first luma transform coefficientof the block of luma transform coefficients using a first scaling valuefrom the luma scaling matrix and based on the second QP value;dequantize the second luma transform coefficient of the block of lumatransform coefficients using a second scaling value from the lumaquantization matrix and based on the second QP value; determine a lumaresidual block for the block of video data based on the firstdequantized luma transform coefficients and the second dequantized lumatransform coefficient; add the luma residual block to a luma predictionblock to determine a decoded luma block, wherein the decoded video dataincludes the decoded luma block.

Clause 47: A method of encoding video data, the method comprising: inresponse to determining that a component of video data is encoded in amode where the component of video data is independently decodable,setting a syntax element indicating whether chroma scaling matrices aresignaled for the video data to a value indicating that the chromascaling matrices are not signaled for the video data; and outputting ina bitstream of encoded video data, an indication of the value for thesyntax element.

Clause 48: The method of clause 47, wherein determining that thecomponent of video data is encoded in the mode where the component ofvideo data is independently decodable comprises determining that thevideo data is encoded in a separate color plane coding mode.

Clause 49: The method of clause 47 or 48, wherein the video datacomprises 4:4:4 video data.

Clause 50: A device for encoding video data, the device comprising: amemory configured to store video data; one or more processorsimplemented in circuitry and configured to: in response to determiningthat a component of video data is encoded in a mode where the componentof video data is independently decodable, set a syntax elementindicating whether chroma scaling matrices are signaled for the videodata to a value indicating that the chroma scaling matrices are notsignaled for the video data; and output in a bitstream of encoded videodata, an indication of the value for the syntax element.

Clause 51: The device of clause 50, wherein to determine that thecomponent of video data is encoded in the mode where the component ofvideo data is independently decodable, the one or more processors arefurther configured to determine that the video data is encoded in aseparate color plane coding mode.

Clause 52: The device of clause 50 or 51, wherein the video datacomprises 4:4:4 video data.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the terms “processor” and “processingcircuitry,” as used herein may refer to any of the foregoing structuresor any other structure suitable for implementation of the techniquesdescribed herein. In addition, in some aspects, the functionalitydescribed herein may be provided within dedicated hardware and/orsoftware modules configured for encoding and decoding, or incorporatedin a combined codec. Also, the techniques could be fully implemented inone or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding a bitstream of encoded videodata, the method comprising: receiving, from the bitstream of encodedvideo data, a first syntax element indicating that the encoded videodata is encoded using a 4:4:4 chroma subsampling format; in response tothe first syntax element indicating that the encoded video data isencoded using the 4:4:4 chroma subsampling format, receiving, from thebitstream of encoded video data, a second syntax element indicatingwhether chroma scaling matrices are signaled separately for chromacomponents of the encoded video data, wherein the first syntax elementis different than the second syntax element, wherein the second syntaxelement has one of at least two different values and wherein a firstvalue of the at least two different values for the second syntax elementindicates the chroma scaling matrices are signaled separately for thechroma components of the encoded video data and a second value of the atleast two different values for the second syntax element indicates thechroma scaling matrices are not signaled separately for the chromacomponents of the encoded video data; in response to the second syntaxelement being equal to the first value indicating that the chromascaling matrices are signaled separately for the chroma components ofthe encoded video data, determining a chroma scaling matrix for a blockof the encoded video data; determining a block of chroma transformcoefficients for the block, wherein the block of chroma transformcoefficients comprises at least a first chroma transform coefficient anda second chroma transform coefficient; determining a quantizationparameter (QP) value for the block of chroma transform coefficients;dequantizing the first chroma transform coefficient of the block ofchroma transform coefficients using a first scaling value from thechroma scaling matrix and based on the QP value; dequantizing the secondchroma transform coefficient of the block of chroma transformcoefficients using a second scaling value from the chroma scaling matrixand based on the QP value, wherein the second scaling value is differentthan the first scaling value; determining a chroma residual block forthe block based on the first dequantized chroma transform coefficientsand the second dequantized chroma transform coefficient; adding thechroma residual block to a chroma prediction block to determine adecoded chroma block; and outputting decoded video data that includesthe decoded chroma block.
 2. The method of claim 1, wherein determiningthe chroma scaling matrix for the block of video data comprisesreceiving the chroma scaling matrix in a parameter set syntax structure.3. The method of claim 2, wherein the parameter set syntax structurecomprises an adaptation parameter set syntax structure.
 4. The method ofclaim 1, further comprising: adding the chroma residual block to thechroma prediction block to determine a reconstructed chroma block; andapplying one or more filters to the reconstructed chroma block todetermine the decoded chroma block.
 5. The method of claim 1, whereinthe block of video data is coded in a separate color plane coding mode.6. The method of claim 1, further comprising: selecting the firstscaling value based on a frequency of the first chroma transformcoefficient; and selecting the second scaling value based on a frequencyof the second chroma transform coefficient.
 7. The method of claim 1,wherein the video data comprises first video data associated with afirst parameter set, the method further comprising: receiving a thirdsyntax element indicating whether second chroma scaling matrices areseparately signaled for chroma components of second video dataassociated with a second parameter set; and in response to determiningthat the second chroma scaling matrices are not separately signaled forthe chroma components of the second video data, determining a lumascaling matrix for a block of the second video data without receiving acorresponding chroma scaling matrix.
 8. The method of claim 1, whereindetermining the chroma scaling matrix for the block of the encoded videodata comprise receiving a set of chroma scaling matrices syntaxelements, the method further comprising: receiving a set of luma scalingmatrices syntax elements, wherein the set of luma scaling matricessyntax elements is a different set of syntax elements than the set ofchroma scaling matrices syntax elements; determining a luma scalingmatrix for the block of video data based on the set of luma scalingmatrices syntax elements; determining a block of luma transformcoefficients for the block of video data, wherein the block of lumatransform coefficients comprises at least a first luma transformcoefficient and a second luma transform coefficient; determining asecond quantization parameter (QP) value for the block of luma transformcoefficients; dequantizing the first luma transform coefficient of theblock of luma transform coefficients using a first scaling value fromthe luma scaling matrix and based on the second QP value; dequantizingthe second luma transform coefficient of the block of luma transformcoefficients using a second scaling value from the luma quantizationmatrix and based on the second QP value; determining a luma residualblock for the block of video data based on the first dequantized lumatransform coefficients and the second dequantized luma transformcoefficient; and adding the luma residual block to a luma predictionblock to determine a decoded luma block, wherein the decoded video dataincludes the decoded luma block.
 9. A device for decoding video data,the device comprising: a memory configured to store video data; one ormore processors implemented in circuitry and configured to: receive,from the bitstream of encoded video data, a first syntax elementindicating that the encoded video data is encoded using a 4:4:4 chromasubsampling format; in response to the first syntax element indicatingthat the encoded video data is encoded using the 4:4:4 chromasubsampling format, receive, from the bitstream of encoded video data, asecond syntax element indicating whether chroma scaling matrices aresignaled separately for chroma components of the encoded video data,wherein the first syntax element is different than the second syntaxelement, wherein the second syntax element has one of at least twodifferent values and wherein a first value of the at least two differentvalues for the second syntax element indicates the chroma scalingmatrices are signaled separately for the chroma components of theencoded video data and a second value of the at least two differentvalues for the second syntax element indicates the chroma scalingmatrices are not signaled separately for the chroma components of theencoded video data; in response to the second syntax element being equalto the first value indicating that chroma scaling matrices are signaledseparately for the chroma components of the encoded video data,determine a chroma scaling matrix for a block of the encoded video data;determine a block of chroma transform coefficients for the block,wherein the block of chroma transform coefficients comprises at least afirst chroma transform coefficient and a second chroma transformcoefficient; determine a quantization parameter (QP) value for the blockof chroma transform coefficients; dequantize the first chroma transformcoefficient of the block of chroma transform coefficients using a firstscaling value from the chroma scaling matrix and based on the QP value;dequantize the second chroma transform coefficient of the block ofchroma transform coefficients using a second scaling value from thechroma scaling matrix and based on the QP value, wherein the secondscaling value is different than the first scaling value; determine achroma residual block for the block based on the first dequantizedchroma transform coefficients and the second dequantized chromatransform coefficient; add the chroma residual block to a chromaprediction block to determine a decoded chroma block; and output decodedvideo data that includes the decoded chroma block.
 10. The device ofclaim 9, wherein to determine the chroma scaling matrix for the block ofvideo data, the one or more processors are further configured to receivethe chroma scaling matrix in a parameter set syntax structure.
 11. Thedevice of claim 10, wherein the parameter set syntax structure comprisesan adaptation parameter set syntax structure.
 12. The device of claim 9,wherein the one or more processors are further configured to: add thechroma residual block to the chroma prediction block to determine areconstructed chroma block; and apply one or more filters to thereconstructed chroma block to determine the decoded chroma block. 13.The device of claim 9, wherein the block of video data is coded in aseparate color plane coding mode.
 14. The device of claim 9, wherein theone or more processors are further configured to: select the firstscaling value based on a frequency of the first chroma transformcoefficient; and select the second scaling value based on a frequency ofthe second chroma transform coefficient.
 15. The device of claim 9,wherein the video data comprises first video data associated with afirst parameter set, wherein the one or more processors are furtherconfigured to: receive a third syntax element indicating whether secondchroma scaling matrices are separately signaled for chroma components ofsecond video data associated with a second parameter set; and inresponse to determining that the second chroma scaling matrices are notseparately signaled for the chroma components of the second video data,determine a luma scaling matrix for a block of the second video datawithout receiving a corresponding chroma scaling matrix.
 16. The deviceof claim 9, wherein to determine the chroma scaling matrix for the blockof the encoded video data, the one or more processors are furtherconfigured to receive a set of chroma scaling matrices syntax elements,and wherein the one or more processors are further configured to:receive a set of luma scaling matrices syntax elements, wherein the setof luma scaling matrices syntax elements is a different set of syntaxelements than the set of chroma scaling matrices syntax elements;determine a luma scaling matrix for the block of video data based on theset of luma scaling matrices syntax elements; determine a block of lumatransform coefficients for the block of video data, wherein the block ofluma transform coefficients comprises at least a first luma transformcoefficient and a second luma transform coefficient; determine a secondquantization parameter (QP) value for the block of luma transformcoefficients; dequantize the first luma transform coefficient of theblock of luma transform coefficients using a first scaling value fromthe luma scaling matrix and based on the second QP value; dequantize thesecond luma transform coefficient of the block of luma transformcoefficients using a second scaling value from the luma quantizationmatrix and based on the second QP value; determine a luma residual blockfor the block of video data based on the first dequantized lumatransform coefficients and the second dequantized luma transformcoefficient; and add the luma residual block to a luma prediction blockto determine a decoded luma block, wherein the decoded video dataincludes the decoded luma block.
 17. The device of claim 9, wherein thedevice comprises a wireless communication device, further comprising areceiver configured to receive encoded video data.
 18. The device ofclaim 17, wherein the wireless communication device comprises atelephone handset and wherein the receiver is configured to demodulate,according to a wireless communication standard, a signal comprising theencoded video data.
 19. The device of claim 9, further comprising adisplay configured to display decoded video data.
 20. The device ofclaim 9, wherein the device comprises one or more of a camera, acomputer, a mobile device, a broadcast receiver device, or a set-topbox.
 21. A non-transitory computer-readable storage medium storinginstructions that when executed by one or more processors cause the oneor more processors to: receive, from the bitstream of encoded videodata, a first syntax element indicating that the encoded video data isencoded using a 4:4:4 chroma subsampling format; in response to thefirst syntax element indicating that the encoded video data is encodedusing the 4:4:4 chroma subsampling format, receive, from the bitstreamof encoded video data, a second syntax element indicating whether chromascaling matrices are signaled separately for chroma components of theencoded video data, wherein the first syntax element is different thanthe second syntax element, wherein the second syntax element has one ofat least two different values and wherein a first value of the at leasttwo different values for the second syntax element indicates the chromascaling matrices are signaled separately for the chroma components ofthe encoded video data and a second value of the at least two differentvalues for the second syntax element indicates the chroma scalingmatrices are not signaled separately for the chroma components of theencoded video data; in response to the second syntax element being equalto the first value indicating that chroma scaling matrices are signaledseparately for the chroma components of the encoded video data,determine a chroma scaling matrix for a block of the encoded video data;determine a block of chroma transform coefficients for the block,wherein the block of chroma transform coefficients comprises at least afirst chroma transform coefficient and a second chroma transformcoefficient; determine a quantization parameter (QP) value for the blockof chroma transform coefficients; dequantize the first chroma transformcoefficient of the block of chroma transform coefficients using a firstscaling value from the chroma scaling matrix and based on the QP value;dequantize the second chroma transform coefficient of the block ofchroma transform coefficients using a second scaling value from thechroma scaling matrix and based on the QP value, wherein the secondscaling value is different than the first scaling value; determine achroma residual block for the block based on the first dequantizedchroma transform coefficients and the second dequantized chromatransform coefficient; add the chroma residual block to a chromaprediction block to determine a decoded chroma block; and output decodedvideo data that includes the decoded chroma block.
 22. Thenon-transitory computer-readable storage medium of claim 21, wherein todetermine the chroma scaling matrix for the block of video data, theinstructions are configured to cause the one or more processors toreceive the chroma scaling matrix in a parameter set syntax structure.23. The non-transitory computer-readable storage medium of claim 22,wherein the parameter set syntax structure comprises an adaptationparameter set syntax structure.
 24. The non-transitory computer-readablestorage medium of claim 21, wherein the one or more processors arefurther configured to: add the chroma residual block to the chromaprediction block to determine a reconstructed chroma block; and applyone or more filters to the reconstructed chroma block to determine thedecoded chroma block.
 25. The non-transitory computer-readable storagemedium of claim 21, wherein the block of video data is coded in aseparate color plane coding mode.
 26. The non-transitorycomputer-readable storage medium of claim 21, wherein the one or moreprocessors are further configured to: select the first scaling valuebased on a frequency of the first chroma transform coefficient; andselect the second scaling value based on a frequency of the secondchroma transform coefficient.
 27. The non-transitory computer-readablestorage medium of claim 21, wherein the video data comprises first videodata associated with a first parameter set, wherein the one or moreprocessors are further configured to: receive a third syntax elementindicating whether second chroma scaling matrices are separatelysignaled for chroma components of second video data associated with asecond parameter set; and in response to determining that the secondchroma scaling matrices are not separately signaled for the chromacomponents of the second video data, determine a luma scaling matrix fora block of the second video data without receiving a correspondingchroma scaling matrix.
 28. The non-transitory computer-readable storagemedium of claim 21, wherein to determine the chroma scaling matrix forthe block of the encoded video data, the instructions cause the one ormore processors to receive a set of chroma scaling matrices syntaxelements, and wherein the instructions further cause the one or moreprocessors to: receive a set of luma scaling matrices syntax elements,wherein the set of luma scaling matrices syntax elements is a differentset of syntax elements than the set of chroma scaling matrices syntaxelements; determine a luma scaling matrix for the block of video databased on the set of luma scaling matrices syntax elements; determine ablock of luma transform coefficients for the block of video data,wherein the block of luma transform coefficients comprises at least afirst luma transform coefficient and a second luma transformcoefficient; determine a second quantization parameter (QP) value forthe block of luma transform coefficients; dequantize the first lumatransform coefficient of the block of luma transform coefficients usinga first scaling value from the luma scaling matrix and based on thesecond QP value; dequantize the second luma transform coefficient of theblock of luma transform coefficients using a second scaling value fromthe luma quantization matrix and based on the second QP value; determinea luma residual block for the block of video data based on the firstdequantized luma transform coefficients and the second dequantized lumatransform coefficient; and add the luma residual block to a lumaprediction block to determine a decoded luma block, wherein the decodedvideo data includes the decoded luma block.